In a unicast only communications system, messages intended for a plurality of receiving subscribers are typically transmitted to each receiving subscriber by way of duplicating each message at or near the originating subscriber's terminal. Thus, in a typical unicast system, transmitting a multicast message is substantially identical to transmitting the same message multiple times from an originating subscriber to each individual recipient in a point-to-point fashion. These redundant transmissions consume bandwidth and other system resources as each message is separately routed through the communications network. Some terrestrial communication systems attempt to reduce the overall resources required to transmit multicast messages through the use of routers and other processing assets which incorporate increased complexity as additional logic is used to control and optimize the message traffic routed through the communications network.
In a satellite communications system, where subscribers communicate through a network of satellite communications nodes, ground-to-satellite (uplink) and satellite-to-ground (down link) resources are often limited. Thus, redundant transmissions of messages from originating subscriber units are highly undesirable. Additionally, it is often weight, power, and cost prohibitive to introduce complex routing logic on board satellite communications nodes. Further, in a satellite communications system which involves satellites in motion relative to terrestrial based subscribers, each satellite must frequently update its own routing table as subscribers are handed off from one satellite communications node to another. Therefore, since each satellite must manage a dynamically changing list of users, this adds significant complexity to each satellite communications node. For the above reasons, terrestrial multicast routing schemes are unlikely to benefit satellite communications systems where each satellite moves relative to the terrestrial based users due to the desire to reduce complexity on board each satellite communications node.
Therefore, it is highly desirable to employ a method and system for conducting multicast sessions customized for use with a satellite communications network. It is also highly desirable to devise a method for managing multicast in a way that decreases the amount of uplink and down link bandwidth required to conduct multicast sessions.